1. Field of the Invention
The present invention relates to a network system for constructing a home network environment, and more particularly, to a data transmitting node and a network inter-connection node suitable for use in the home network environment.
2. Description of the Background Art
In recent years, there is a rapid trend for digitalizing electronic instruments as exemplified by the term “multi-media”, and this trend is already noticeable in the office environment.
More specifically, in terms of hardware, this trend has been materialized in forms of introduction of PCs, digitalization of OA devices and formation of networks among them. Also, in terms of software, this trend has been expanding to cover the basic functions of hosts (which are progressively light-sized and transferred to PCs), the application software such as the word-processing software, the spreadsheet software, etc., and the Internet application such as the WWW.
The similar trend can also be seen in the home environment. Namely, even in the home environment, this trend for digitalization has been steadily progressed in forms of digitalization of AV devices (DVD, digital VTR, digital video camera, etc.), digitalization of broadcasting, and Internet access such as OCN.
Similarly as in a case of the office environment, this trend is expected to progress toward the formation of networks in future. Namely, it is expected that the technologies of various fields such as information processing, communication and broadcasting will be unified by the digitalization, and inter-mixed with each other by the formation of networks.
There are many candidates for the network technologies in this direction. For example, the Ethernet has overwhelming records of the actual use in the office environment and is probably the most promising candidate even for the home PC network. Also, the ATM is another serious contender because of the general consensus among the infra-structure constructors (telephone companies, CATV companies, etc.) to keep constructing the infra-structures based on this technology in view of the advantageous characteristics of the ATM such as its fast, real-time, and wide bandwidth properties.
In addition to these candidates, the network technology (bus technology) called IEEE 1394 has been attracting much attentions recently. This IEEE 1394 has several remarkable characteristics such as its fast, real-time (QOS guaranteed), and plug-and-play properties, so that there is a high expectation especially among the AV industries on the IEEE 1394 as the most promising candidate for a future scheme for inter-connecting digital AV devices. This vogue has also instigated much interests to the IEEE 1394 from the computer industries as well.
In the initial phase, it is expected that the inter-connection of the home use digital devices will be realized by these various network technologies in conjunction with the spread of the home use digital devices, depending on preferences and demands of the users, and in this way prototype digital networks will be gradually built up inside each home.
In the second phase, there will be demands for inter-connecting these digital networks together. For example, there will be a desire to inter-connect an AV device connected to the 1394 network of a guest room on the first floor with another AV device connected to the 1394 network of a private room on the second floor in order to realize the dubbing or the cooperative operation between these AV devices.
However, in order to meet the expected demands of this second phase, the following problems must be addressed and resolved.
(1) The 1394 network is not suited for a large scale installation. For example, its cable length is limited to 4.5 m, so that the wiring across rooms will be difficult. Also, the plug-and-play function of the 1394 has the side-effect that the on-going communication will be instantaneously disconnected whenever someone connects to or disconnects from the 1394. When the wiring of the 1394 across rooms is attempted, there will be an inconveniency in that an action made in one room would affect another room in a form of the instantaneous disconnection of the on-going communication because of its “bus reset”.
(2) The standardization of the specification for “1394bridge” as the inter-connection protocol/scheme for the 1394 is currently in progress at the IEEE which is the standardization committee for the 1394. However, the standard specification is expected to be a very complicated one that requires the scalability and incorporates a concept of call set up, and it is also expected that a considerable amount of time will be needed before the standard specification can be solidified.
(3) The home network will not necessarily be limited to just the 1394, so that it is preferable to construct the home network according to a scheme that can inter-connect various types of networks. However, no such a network architecture has been proposed so far.
(4) As a known technique for inter-connecting various networks, there is the Internet protocol. However, this scheme is difficult to set up, manage and maintain for the layman, and it also requires the server management, so that in its currently available form it is not suitable for an inter-connection scheme intended for use in the home network which is expected to deal with a rather limited number of terminals.
On the other hand, in recent years, rapid progresses made in-the communication technology such as Internet are attracting much attentions from various fields, and issues such as introduction of LAN or connection of that to WAN or Internet are much discussed mainly among companies and universities.
These technological innovations are highly likely to change the network environment surrounding our homes. Namely, with the spread of various digital devices such as PC, DVD, digital set-top box and so on in our homes, demands for inter-connecting them through a digital network inevitably arises. Currently, IEEE 1394 bus is attracting much attentions from various fields, especially among AV vendors, as a prime candidate for such a digital network for home use.
This IEEE 1394 bus can be used as a high speed digital network of 100, 200 or 400 Mbps, and has several remarkable characteristics including plug-and-play properties, synchronous transfer function using isochronous channel, etc., as already mentioned above.
Meanwhile, rapid technological innovations are also made in the so called access network for homes. Namely, notable progresses have been made in high speed network technologies such as CATV, ADSL (Asymmetric Digital Subscriber Line) and FTTH (Fiber-To-The-Home) as well as network services such as Internet, and so on. In particular, the Internet technology has promoted many remarkable techniques including its fast implementation, guarantee of QOS (Quality Of Service) using network layer level signaling protocol such as RSVP (Resource Reservation Protocol), multicast, and so on.
In near future where these techniques are realized on Internet, transfer of some information that require high speed and realtime characteristics such as video transfer to homes may very well be carried out through Internet. This is because Internet can store virtually infinite amount of information so that it is only natural for Internet users to come to expect acquisition through Internet of the above noted information which has conventionally been acquired from terrestrial or satellite broadcasting and the like.
However, when exchanges of information through Internet are attempted by-connecting home digital devices through the access network, the following problems will be encountered.
(1) Currently, a scheme for distributing Internet data over IEEE 1394, i.e., IP-over-1394, is discussed by various groups, but these discussions still remain at a level of the so called address resolution scheme. On the other hand, there is a proposition of a signaling protocol such as-RSVP for carrying out data exchanges with guaranteed communication quality on Internet. However, a scheme for operating such a network layer signaling protocol on IEEE 1394 has not been standardized so that mapping to a transfer scheme that does not guarantee communication quality is the only available option for IEEE 1394.
Consequently, even when the above noted signaling protocol is executed, data will be transferred over IEEE 1394 on the best effort basis (more specifically, through asynchronous channel) so that the end-to-end communication quality cannot be guaranteed.
(2) In the case of transmission and reception of IP multicast on IEEE 1394 bus, the use-of isochronous channel or asynchronous stream of IEEE 1394 can be considered in order to minimize traffic on IEEE 1394 bus. However, when two or more devices tries to subscribe for the same IP multicast at the same time, there is a possibility for these two or more devices to reserve different channels separately so that the efficient utilization of communication resource cannot be realized.
Moreover, there is no mechanism for enabling synchronized recognition of correspondence between reserved channel and IP multicast address by a transmitting side and a receiving side.